At present, the flexible absorbing materials and wave absorbing bodies that are being developed and put into practice abroad mainly include the following:
Ferrite series flexible absorbing material (nickel-zinc ferrite, manganese-zinc ferrite, barium ferrite, etc.): due to the resonance absorption of ferromagnetic materials and the dispersion effect of magnetic permeability, the ferrite flexible absorbing material has the advantages of strong absorption and wide frequency band, and is widely used in various stealth technology fields. The ferrite flexible absorbing material researched by Japan’s NEC company is composed of two layers with a thickness of 3.8mm and 0.9mm, the mass per unit area is 8kg/m2, the bandwidth of attenuation -20dB is 8.5~12.2GHz, and the bandwidth of attenuation -10dB is 6~13GHz .
Micro-powder flexible absorbing material: Micro-powder materials (especially nano-wave absorbing materials) are valued by all aspects due to their peculiar physical and chemical properties. They have low reflection and high absorption of electromagnetic waves, and are a new material worthy of attention. In the particles of the ultrafine powder material, the surface atoms account for a large proportion of the whole particle atoms, and the surface atoms have more dangling bonds and empty bonds, and their activity is greatly increased. When electromagnetic waves are incident on such particles, the movement of molecules and electrons is intensified, the efficiency of converting electromagnetic energy into heat energy is high, and the electromagnetic loss is large. Its transmission and absorption properties depend on the particle size. This feature can be used to achieve the purpose of inter-layer turn matching and broadening the frequency band. For example, the electromagnetic wave absorber made of nano-silicon carbide fiber as the base material has a bandwidth of -15dB absorption in the frequency range of 8 to 12GHz, and the absorption bandwidth is greater than 1GHz. The specially treated carbon fiber has good application value in the radar band. For metal powders such as hydroxy Fe powder, Ni powder, Co powder, the particle size is generally between 10 and 50 nm, which has also been widely studied, but its applicability is limited due to its poor anti-oxidation properties.
Polycrystalline ferromagnetic metal fibers: Polycrystalline ferromagnetic metal fibers have unique shape characteristics and recombination loss mechanisms (magnetic and dielectric losses). It has the advantages of light weight (density <2kg/m2), wide frequency band (4～18GHz) and good oblique incidence performance. And the electromagnetic parameters of the absorber can be adjusted by adjusting the length, diameter and arrangement of the fibers, which is a kind of absorbing material worthy of research.
Schickoff salt-based retinoid: black like graphite, better absorbing properties than other materials, and only 1/10 of the weight of iron ball absorbing materials. The absorbing frequency bandwidth of this material is effective from long wave to 8mm band. It converts all electromagnetic wave energy into heat energy through ion displacement, but the temperature rise of the material itself is not obvious.
Dielectric ceramic absorbing materials: PZT (lead zirconate titanate), BaTiO3 and other dielectric materials also have good absorbing effect, but the absorption bandwidth is small.
Conductive polymer material: Compared with other absorbing materials, it has the characteristics of low density (only 1/5 of ferrite), and its absorbing performance is controlled by adjusting the conductivity by doping. Foreign reports have a bandwidth of -10dB and 12GHz in the millimeter waveband.
Chiral flexible absorbing material: Compared with ordinary materials, its biggest feature has chiral parameters, and the electromagnetic waves propagating in it can only be left-handed or right-handed circularly polarized waves. Its advantage is that the impedance matching can be adjusted by adjusting the chiral parameters, and it is much easier than adjusting μ and ε; in addition, it has low frequency sensitivity and is easy to achieve broadband absorption. Once there is a breakthrough in the practical technology of flexible absorbing material, it will have a significant impact on EMC technology.
Electromagnetic wave absorber
The above types of flexible absorbing materials are the main absorbing materials currently researched and developed. However, at the current level of research and production, it is unrealistic to use a single material as an absorber to achieve broadband absorption, and it cannot solve the problem of non-reflection. In practical applications, a single material and direct use are generally less used, but in the form of electromagnetic wave absorbers.
The electromagnetic wave absorber is a structured electromagnetic wave absorbing material for the best electromagnetic wave absorption effect, and it can appear in the form of commercial products. Internationally, composite and structural design methods are used to solve the absorption problem of a certain frequency band, and it is the first to be applied in military applications. Stealth aircraft such as B-2, YF-22, and YF-23 all use structured absorbers.
The research on electromagnetic wave absorbers is based on the research on absorbing materials. At present, the practical absorber structures are as follows:
- Single-layer structure: It is a single-coating and single-layer absorber that behaves as a composite material.
- Multi-layer structure: It consists of a wave-transmitting layer, an impedance matching layer, an absorbing layer and a reflective backing. In the design, the mutual cancellation technology of the incident wave and the reflected wave is often used. Although the corresponding absorption peak will appear at this time, the absorption bandwidth will be affected.
Shenzhen PH Functional Materials has been engaged in the production of electromagnetic wave absorption and shielding materials for many years. We have rich production experience. Popular products mainly include flexible absorbing materials, emc absorber, nfc absorber, etc. If you want to know more product information, please contact us.
